Figure 4.

Activation of H₃R with the selective agonist imetit (100 nM) attenuates both Ca²⁺ influx and resulting exocytosis of tritiated norepinephrine (NE) in K⁺-depolarized, cultured neuroblastoma cells transfected with the H₃R (SH-SY5Y-H₃; B and D). Parent SH-SY5Y cells fail to respond to imetit (A and C). (Upper) Release of [³H]norepinephrine from SH-SY5Y cells (A) and SH-SY5Y-H₃ cells (B), by depolarization with 10–100 mM K⁺, in the absence and presence of imetit (100 nM), either alone or in combination with the selective H₃R antagonist thioperamide (300 nM; B). Points represent mean [³H]norepinephrine release expressed as a percentage of total [³H]norepinephrine content (± SEM; n = 3–7). *, P < 0.05 from the corresponding control [³H]norepinephrine level by unpaired t test. (Lower) Peak Ca_i concentration in SH-SY5Y cells (C) and SH-SY5Y-H₃ cells (D) depolarized with 100 mM K⁺ in the absence and presence of imetit ± thioperamide (D). Bars represent means (± SEM) of 157 control and 174 imetit-treated SH-SY5Y cells (C), and 232 control, 197 imetit-treated, and 231 imetit + thioperamide-treated SH-SY5Y-H₃ cells (D). *, P < 0.05 from the corresponding control peak Ca_i level by unpaired t test.